Method and apparatus for waveform measurement instrument

ABSTRACT

Sampling techniques and circuits for a waveform measuring instrument. The sampling techniques and circuits process a series of digital signal samples through a set of sample extractors and subsequently process the extracted digital signal samples. The set of sample extractors include a uniform decimator, a low frequency dither decimator, and a digital peak detector. The uniform decimator extracts a uniform decimated sample value for each decimated sample interval in a series of decimated sample intervals. The low frequency dither decimator extracts a low frequency dither decimated (random) sample value for each decimated sample interval in a series of decimated sample intervals. The digital peak detector extracts a maximum sample value and a minimum sample value for each decimated sample interval in the series of decimated sample intervals. The subsequent processing of the samples includes selecting samples from the set of extracted samples, storing the selected samples, retrieving the selected samples, potentially manipulating the selected samples mathematically or analytically interpreting the selected samples, and displaying the manipulated or analyzed sample values.

FIELD OF THE INVENTION

[0001] This invention relates generally to the field of waveformmeasurement and sampling. More particularly, this invention relates totechniques and circuits for sampling waveforms in a waveform measurementinstrument.

BACKGROUND OF THE INVENTION

[0002] The field of digitally sampled waveform measurement recognizesseveral issues that affect how a signal can be reconstructed, measured,and displayed after it has been sampled and stored. Some of these issuesare aliasing, glitch detection, etc. Aliasing of a signal occurs whenthe frequency of sampling of a signal is less than twice the frequencyof the highest frequency component of the signal, as proven by Nyquist,and results in improper reconstruction and frequency domainrepresentation of the signal from its discrete time samples. Glitchescan go undetected without sufficient measures to capture the glitchinformation.

[0003] One side effect of the requirement to sample a signal at twiceits highest frequency is that a large amount of storage can be required.Solutions exist that reduce the storage requirement by selectivelystoring only some of the signal information that is sampled while stillpreserving much of the high frequency information. For example, for agiven sample interval in time, an existing solution stores only theminimum signal value, the maximum signal value, and a decimated samplevalue for that interval. By storing only a minimum, maximum, anddecimated sample for each time interval rather than storing each sample,the existing solution effectively reduces the amount of storage neededfor each time interval to effectively reconstruct the signal.

[0004] The minimum and maximum values stored in each time intervalassure that glitches can be reconstructed within the time interval. Adecimated sample value can be a signal sample that is randomly chosen(dither decimated) from each time interval or a sample from the sameposition (uniform) in each time interval, but not both. When a uniformdecimator is used, aliasing can result because of the reduced number ofsamples that the compression algorithm stores (for signalreconstruction, behaves like sampling at a lower frequency). When adither decimator is used, aliasing is effectively reduced, but certainmathematical functions such as a Fast Fourier Transform (FFT) cannot beperformed and others become computationally expensive. A FFT cannot beperformed with a dither decimated sampling algorithm because thesampling interval must be uniform for this frequency based mathematicaloperation to be applicable.

BRIEF SUMMARY OF THE INVENTION

[0005] The present invention relates generally to techniques andcircuits for digitally sampling waveforms in a waveform measurementinstrument. Objects, advantages and features of the invention willbecome apparent to those skilled in the art upon consideration of thefollowing detailed description of the invention.

[0006] A sampling technique for a waveform measuring instrument,consistent with certain embodiments of the present invention involvesprocessing a series of digital signal samples through a uniformdecimator to extract at least one uniform decimated sample value foreach sample interval in a first series of sample intervals; processingthe series of digital signal samples through a low frequency ditherdecimator to extract at least one low frequency dither decimated samplevalue for each sample interval in a second series of sample intervals;and processing the series of digital signal samples through a digitalpeak detector to extract a maximum sample value and a minimum samplevalue for each sample interval in the third series of sample intervals.In certain embodiments, the process further involves carrying out areducing process by: processing the retrieved signal samples through areducer uniform decimator to extract at least one uniform decimatedsample value for each sample interval in a fourth series of sampleintervals; processing the retrieved signal samples through a reducer lowfrequency dither decimator to extract at least one low frequency ditherdecimated sample value for each sample interval in a fifth series ofsample intervals; and processing the retrieved signal samples through areducer digital peak detector to extract a maximum sample value and aminimum sample value for each sample interval in a sixth series ofsample intervals.

[0007] Many variations, equivalents and permutations of theseillustrative exemplary embodiments of the invention will occur to thoseskilled in the art upon consideration of the description that follows.The particular examples above should not be considered to define thescope of the invention.

BRIEF DESCRIPTION OF THE DRAWINGS

[0008] The features of the invention believed to be novel are set forthwith particularity in the appended claims. The invention itself however,both as to organization and method of operation, together with objectsand advantages thereof, may be best understood by reference to thefollowing detailed description of the invention, which describes certainexemplary embodiments of the invention, taken in conjunction with theaccompanying drawings in which:

[0009]FIG. 1 is a block diagram of a waveform measurement instrumentarchitecture consistent with certain embodiments of the presentinvention.

[0010]FIG. 2A is a first portion of a first flow chart of a waveformmeasurement instrument architecture consistent with certain embodimentsof the present invention.

[0011]FIG. 2B is a second portion of a first flow chart of a waveformmeasurement instrument architecture consistent with certain embodimentsof the present invention.

[0012]FIG. 3 is a block diagram of another waveform measurementinstrument architecture consistent with certain embodiments of thepresent invention.

[0013]FIG. 4A is a first portion of a second flow chart of anotherwaveform measurement instrument architecture consistent with certainembodiments of the present invention.

[0014]FIG. 4B is a second portion of a second flow chart of anotherwaveform measurement instrument architecture consistent with certainembodiments of the present invention.

[0015]FIG. 5 is a computer system consistent with certain embodiments ofthe present invention.

DETAILED DESCRIPTION OF THE INVENTION

[0016] While this invention is susceptible of embodiment in manydifferent forms, there is shown in the drawings and will herein bedescribed in detail specific embodiments, with the understanding thatthe present disclosure is to be considered as an example of theprinciples of the invention and not intended to limit the invention tothe specific embodiments shown and described. In the description below,like reference numerals are used to describe the same, similar orcorresponding parts in the several views of the drawing.

[0017] Turning now to FIG. 1, a waveform measurement instrumentarchitecture 100 such as that used in a digital oscilloscope is shown.In this figure, processor 104 controls and manipulates the output of thevarious components of the architecture as described below. An inputsignal is converted to a digital representation with the use of theanalog to digital (A/D) converter 108. Each sample produced by the A/Dconverter 108 represents a sample of the input signal at a specificsample time. The A/D converter 108 continuously produces samples takenat regular sampling intervals, forming a stream of digital signalsamples, while the waveform measurement instrument architecture 100 isactive.

[0018] A data compressor 112 operates over successive time intervals(decimated sample intervals) to reduce the amount of digital signalsample storage required by the waveform measurement instrumentarchitecture 100. A time interval (decimated sample interval) can bethought of as a length of time over which the current compressionactivity operates. For purposes of this document, the time intervals fordifferent types of decimation may or may not be the same size and may ormay not be in phase. Moreover, adjacent intervals are not necessarilyadjacent or non-overlapping (but can be). An acquisition time period canbe thought of as the entire acquisition time that is divisible into aset of time intervals. The data compressor 112 reduces the number ofdigital signal samples over the acquisition time period that need to bestored to a memory 116 by selectively choosing certain samples from eachtime interval that will allow aliasing resistant reconstruction of thesignal while also allowing glitch detection and mathematical functionsto be performed on the reconstructed signal.

[0019] The data compressor 112 can store each sample produced by the A/Dconverter 108 during an acquisition time period into the memory 116,as-is and without manipulation, when the acquisition time and availablestorage make this possible. Otherwise, the data compressor 112 acts toenable capture of long acquisition records when the memory 116 is notlarge enough to hold all of the raw data that is obtained over theacquisition time period.

[0020] A digital sample extractor 120 is configured by the processor 104to extract signal information over a time interval from the stream ofdigital signal samples produced by the A/D converter 108. The number ofdigital signal samples over which the digital signal extractor 120operates for a given time interval is a function of the number ofdigital signal samples produced by the A/D converter 108 over that timeinterval (ultimately dictated by sampling rate). The digital signalextractor 120's components extract information from the set ofsequential samples that represent the configured time interval, andrepeat the process again for subsequent time intervals. The digitalsample extractor 120 has a digital peak detector 124, a low frequencydither (LFD) decimator 128, and a uniform decimator 132. The digitalpeak detector 124 repeatedly selects the maximum and minimum signalsample values for the current time interval and can operate in anoverlapped or non-overlapped manner. The low frequency dither (LFD)decimator 128 repeatedly selects a random sample from the current timeinterval using any suitable random or pseudo-random process. The uniformdecimator 132 repeatedly selects a sample from a specific time point inthe current time interval. The processor 104 controls the digital sampleextractor 120 to identify the time interval over which to extract signalinformation.

[0021] For a sequence of time intervals of interest, aliasing resistantreconstruction of the signal, glitch detection (analyticalinterpretation of the sample value extremes against preset thresholds),and mathematical operations upon the reconstructed signal can beperformed with the information represented by the minimum and maximumsample values, the dither decimated sample value, and the uniformdecimated sample. By recognizing this fact, the invention uses the datacompressor 112 to reduce the number of digital signal samples requiredfor aliasing resistant reconstruction of the signal, glitch detection,and mathematical operations. Based upon the fact that the method usesfour signal samples to represent a signal during a sample interval, anyinterval of larger than four samples in length can achieve a netreduction (compression) in its memory storage requirements.

[0022] The compression select multiplexer (MUX) 136 is configured by theprocessor 104. The compression select MUX 136 can store all four digitalsignal samples for each time interval to the memory 116 or it can beconfigured for further reductions in the amount of information storagefor each time interval based upon intentions for the reconstructedsignal. If, for example without limitation, at signal acquisition timethe compression select MUX 136 is configured only to select the minimumand/or maximum (peak detect mode or glitch detect mode) of a signalduring a given time interval, the compression select MUX 136 selectsonly the values generated by the digital peak detector 124. Likewise,if, at signal acquisition time, only a mathematical function (by way ofa mathematical function selection) is intended, then the uniformdecimator 132 output values are selected. Furthermore, if, at signalacquisition time, only an aliasing resistant reconstruction (nomathematical function selection) is intended then the LFD decimator 128output values are selected. Under control of the processor 104, the datacompressor 112, with the compression select MUX 136 can achieve evenfurther reduction in the amount of storage required for a given timeinterval. The resultant set of digital signal samples is stored to thememory 116.

[0023] The memory 116 contains a compressed set of signal samples forthe previous acquisition time period organized as smaller sets of signalsamples for each time interval. A reducer 140 is used to retrieve thesamples from memory 116, optionally further compress and/or selectsubsets by type, and present them for processing by the processor 104.Within the reducer 140, a memory parser 144 is configured by theprocessor 104 to interpret the formation of the sets of signal samplesin the memory 116. The memory parser 144 also sequentially retrievesfrom memory 116 the signal samples for each successive time interval forthe entire acquisition time period or a portion thereof.

[0024] Memory parser 144 of the reducer 140, parses the max and/or minvalues at reducer digital peak detector 148, the LFD decimated values atreducer LFD decimator 152, and the uniform decimated values at reduceruniform decimator 156 from memory 116 for a given time interval andsupplies these values to the reduction select multiplexer (MUX) 160.

[0025] A reduction selection MUX 160 within the reducer 140 isconfigured by the processor 104 to allow a further reduction in each setof signal samples that is retrieved from memory 116 based upon theintended action to be performed upon the sequential sets of signalsamples. This further reduction potentially allows for a reducedbandwidth requirement between the reducer 140 and the processor 104 incertain circumstances when all stored signal data for a givenacquisition time period is not needed for the current processingrequirements. As discussed above for the compression select MUX 136, thereduction selection MUX 160 can selectively pass through either theentire set of signal samples for each time interval or a subset of eachset of signal samples. In any event, the processor 104 receives thesignal samples for each time interval from the reducer 140, reconstructsthe signal, and performs the intended functions on the reconstructedsignal. Once the intended functions (e.g. math functions) have beenperformed on the reconstructed signal, the processor 104 passes theresulting signal representation to the display 164 for presentation.

[0026] The compressor 112 enables capture of long acquisition recordswhen the memory is not large enough to hold all of the raw data that isobtained over the acquisition time. The reducer 140, on the other hand,carries out a similar function as the compressor 112, but to achieve adifferent objective. The reducer 140 provides fast processing of thestored data by “reducing” the amount of data that has to be transferredto the processor 104 using the same techniques as those used in thecompressor 112. Whether the compression function is carried out in thereducer 140 or compressor 112, applying this algorithm to the storeddata (as well as raw data) greatly speeds processing.

[0027] Stored data can be transferred from memory 116 directly to theprocessor 104 (and this is one mode of operation that is sometimes used)to render a display and/or perform mathematical operations on the datain any desired manner. However, the bandwidth of the processor 104interface and processor computational speed is often limited such thatprocessing of all stored data directly by the processor 104 can take aninordinate amount of time in deep memory systems. The reducer 140addresses these limitations by (1) accessing the data at a speed verymuch greater than the processor 104 can by using dedicated andspecialized digital hardware and (2) reducing (i.e. compressing) thestored data so that less has to be transferred to the processor 104,thus getting around the speed limitation of the processor interface.Both the compressor 112 and reducer 140 serve to “compress” the data.While the compressor 112 compresses to fit the data into availablememory, the reducer 140 compresses so that less data have to betransferred to the processor 104. In addition, a hardware realization ofthe reducer 140 may be able to access memory 116 and perform itscomputations much faster than the processor 104 can do the equivalent.

[0028] The compressor 112 divides the input stream into time intervalsand a dithered decimated value, uniform decimated value, and peak valuesare selected over each time interval and stored to achieve a netcompression. As for the reducer 140, it takes the compressor 112 output(i.e. the data stored in memory 116) processes it in a manner similar tothat used by the compressor 112 in processing raw data. In the simplestcase the compressor 112 just stores the data as-is into memory 116 whenthe acquisition time and available storage make this possible. In thiscase, the reducer 140 uses the exact same algorithms as the compressor112, since it is operating with raw data, and transfers compressed datasets to the processor 104. The point in doing this is to process datafaster than the processor 104 can if it were to process the stored datadirectly. In addition, the reducer 140 can also leave the raw dataunmolested so the processor 104 gets exactly the digitized samples. Inother words, both the compressor 112 and reducer 140 have “do nothing tothe data” modes where raw data are dealt with directly by the processor.

[0029] When the stored data are the compressed form, the reducer 140 canfurther reduce this data so that less data has to be transferred to theprocessor 104. This amounts to a recursive application of thecompression algorithm. To accomplish this, the reducer 140 employs amodified version of the algorithm: First, as mentioned, the stored datais parsed so the reducer 140 can track which data are dither decimated,uniform decimated, minimums, and maximums. The reducer 140 can be set topass only selected subsets of these types, per data set, and reduce theamount of data to be transferred to the processor 104. In addition, thereducer 140 can combine two or more adjacent stored data sets into oneset, with all of the same types (and with the same meanings for thetypes) as the stored data, to deliver an even more compressedrepresentation of all of the data represented by the multiple data setsthat were combined. It does this by streaming the stored data sets to amachine that repeatedly combines every given number (N) of consecutivedata sets into single data sets: For every N data sets input, one dataset is output and transferred to the processor 104. The reduceralgorithm for doing this varies from the compressor algorithm asfollows:

[0030] For the further-compressed (i.e. reduced) uniform-decimatedcomponent, the reducer 140 chooses that same type and always choosesfrom the same data set within each N consecutive input data sets thatare being combined into one data set.

[0031] For the further-compressed (i.e. reduced) dither-decimatedcomponent, the reducer chooses that same type randomly from any one ofthe N consecutive input data sets that are being combined into one dataset

[0032] For the further-compressed (i.e. reduced) minimum and maximumcomponents, the reducer simply takes the minimum and maximum over thevalues of that same type across all N consecutive data sets beingcombined into one data set. (Actually, since the dither and uniformdecimated values can never be smaller than the minimum in a data set,and they also cannot be larger than the maximum, the output minimum andmaximum could be taken over all types instead of just the minimum andmaximum types.) While the reducer can further compress stored data, itcan also simply pass the compressed stored data onto the processor whichis a mode that is sometimes used depending on the purposes at hand.

[0033] It should be noted that at either the compression phase or thereduction phase, not all types need to be carried along depending uponthe purposes at hand. The compressor 112 need not generate and store alltypes and likewise, the reducer 140 need not emit all types and can evendiscard some of the types that have been stored. Note, however, that ifa type has not been stored the reducer 140 cannot recreate it. It shouldalso be noted, that although the previous discussion covers theinclusion of zero or one uniform sample and zero or one dithereddecimated sample, more than one uniform sample and/or more than onedither decimated sample can be generated and still be within the scopeof the present invention. In fact, it may be advantageous to implementthe present invention using an ASIC that has a mode where two uniformdecimated samples are generated along with the minimum and maximum.Multiple uniform samples can be taken from evenly spaced locationsacross the interval and always from the same locations within eachinterval. For multiple dither decimated samples, the interval can bedivided up into a number of equally sized subintervals, this numberbeing equal to the number of dithered samples to generate, and arandomly chosen sample from within each subinterval is taken. Thisapplies for both the compressor 112 and reducer 140. Those skilled inthe art will appreciate, in view of this discussion, that there areother imaginable convolutions such as multiple pairs of peak values,etc.

[0034] It should also be noted that the compressor 112 operates in realtime, and only gets one shot at the data. The reducer 140 operates inpseudo real time, i.e. it operates fast enough to give the user suitablethroughput. Therefore, the reducer 140 may operate multiple times on asingle stored set of data. In fact, it can operate on N differentpreviously stored sets of data (acquisitions). Operating multiple timesmay be the result of the user changing the instrument set-up, forexample, deciding to make a rise time measurement, turning on afunction, or simply panning and/or zooming.

[0035] Given this teaching, a person skilled in the art will recognizethat the list of possible functions that can be performed upon thereconstructed signal include, but are not limited to, simple mathfunctions such as adding an offset (positive or negative), multiplyingthe signal by a constant, functional manipulation of the signal (e.g.fast Fourier transform (FFT)), measurement of signal characteristics,etc. Many other actions on the reconstructed signal are possible andshould be considered within the scope of this invention.

[0036] Turning now to FIG. 2, which is made up of FIG. 2A and FIG. 2B, awaveform measurement method 200 is shown. It may be helpful to refer toFIG. 1 for an architectural application of this method. This methodstarts at 204. At 208, digital signal samples are taken over a samplingtime interval. At 212, the digital signal samples are processed througha uniform decimator to extract at least one sample from a specificposition in every time interval. Simultaneously with 212, at 216, thedigital signal samples are processed through a dither decimator toextract at least one sample randomly (i.e., at a randomly selected timewithin the interval) from the time interval. Likewise, at 220,simultaneously with 212 and 216, the digital signal samples areprocessed through a digital peak detector to extract minimum and maximumsamples from the time interval. As discussed above, extracting this setof samples allows the potential for compression of the data, therebyreducing storage requirements of the method. As well, this approachpreserves the ability to reduce aliasing in a reconstructed signal,while allowing glitch detection and mathematical functions to beperformed on the reconstructed signal.

[0037] At 224 a decision is made about whether to use the raw data, allextracted samples or to select a subset for storage from the extractedsamples. This determination is based upon the desired intent for thestored signal samples. Recalling the discussion in relation to theconfiguration select MUX 136 of FIG. 1, the possibilities for selectionapply here as well. If a selection is intended from the extractedsamples, this is done at 228.

[0038] Once the samples that are intended for storage have beenselected, they are stored to a memory at 232. The stored samples (or rawdata) are then available for processing and can be retrieved from memoryat 236 for processing by reducer 140. In some instances, reducer 140 maysimply pass the data from memory to the processor without furthercompression of the data. At 237, the digital signal samples areprocessed through a uniform decimator to allow the extraction of asample from a specific position in every N time intervals retrieved frommemory 116. Simultaneously with 237, at 238, the digital signal samplesare processed through a dither decimator to allow the extraction of asample randomly from every N time intervals. Likewise, at 239,simultaneously with 237 and 238, the digital signal samples areprocessed through a digital peak detector to allow the extraction ofminimum and maximum samples from every N time intervals. As discussedabove, extracting this set of samples allows the potential forcompression of the data, thereby reducing the bandwidth requirements tothe processor 104. As with the previous discussion, all samples can bepassed through each of these portions of the process, or a subset may bepassed through. If raw data was stored to memory 116 at 232 above, thenraw data can be passed through at this point in the process as well.

[0039] At 240, a decision is made about whether to use all retrievedsamples or to select a subset for processing from the retrieved samples.This determination is based upon the desired intent for the retrievedsignal samples. Recalling the discussion in relation to the reductionselect MUX 160 of FIG. 1, the possibilities for selection apply here aswell. If a selection is intended from the retrieved samples, this isdone at 244.

[0040] The selected retrieved samples are then used to reconstruct thesignal at 248. At 252, a decision is made about whether to perform amathematical function on the reconstructed signal. This decision blockworks in conjunction with the previous two decision blocks, 224 and 240,such that a uniform decimated sample is still present in the selectionset of samples related to the reconstructed signal if a mathematicalfunction is to be performed on the reconstructed signal.

[0041] If a mathematical function is to be performed, this is done at256. As mentioned above, this mathematical function can be, by way ofexample without limitation, simple math functions such as adding anoffset (positive or negative), multiplying the signal by a constant,functional manipulation of the signal (e.g. Fast Fourier Transform(FFT)), measurement of signal characteristics, etc. Many other actionson the reconstructed signal are possible and should be considered withinthe scope of this invention. At 260, the resultant waveform is displayedand the waveform measurement method 200 ends at 264.

[0042] Turning now to FIG. 3, a waveform measurement instrumentarchitecture 300 such as that used in a digital oscilloscope is shown.This figure represents a multichannel architecture similar to thepreviously discussed waveform measurement instrument architecture 100 ofFIG. 1. In this figure, processor 304 controls and manipulates theoutput of the various components of the multi-channel architecture asdescribed below. Each channel in the waveform measurement instrumentarchitecture 300 operates in a manner similar to that of waveformmeasurement instrument architecture 100 of FIG. 1 without the processor104 and without the display 164. As such, when reference is made belowto any components of a given channel, the reader can refer to thediscussion above on waveform measurement instrument architecture 100 ofFIG. 1 for specifics related to the components.

[0043] Architectural element 308 depicts channel 1, while 312 depictschannel 2 of the waveform measurement instrument architecture 300. Itshould be apparent to one skilled in the art that, upon consideration ofthis teaching, the multi-channel nature of this architecture can beextended beyond two channels without departure from the presentinvention. Two channels are discussed here for simplicity ofpresentation and this discussion is not intended to limit the inventionas such.

[0044] An input signal is converted to a digital representation within308 with the use of the analog to digital (A/D) converter 316. Theoutput digital signal samples from the A/D converter 316 are availableto the compressor 320. The compressor 320 operates under the control ofthe processor 304 to selectively store a reduced set of digital signalsamples to the memory 324 based upon criteria discussed above. Under thecontrol of the processor 304, the reducer 328 parses the stored digitalsignal samples from the memory 324 and further reduces the sample settransmitted to the processor 304 based upon criteria discussed above.

[0045] Similarly, an input signal is converted to a digitalrepresentation within 312 with the use of the analog to digital (A/D)converter 332. The output digital signal samples from the A/D converter332 are available to the compressor 336. The compressor 336 operatesunder the control of the processor 304 to selectively store a reducedset of digital signal samples to the memory 340 based upon criteriadiscussed above. Under the control of the processor 304, the reducer 344parses the stored digital signal samples from the memory 340 and furtherreduces the sample set transmitted to the processor 304 based uponcriteria discussed above.

[0046] After the above-described sequence is completed for all channelsof interest, the processor 304, reconstructs the signals for allchannels. After all signals have been reconstructed, processor 304further manipulates the reconstructed signals by implementing anymathematical functions or other processing that may be appropriate forthe given situation. Given this teaching, a person skilled in the artwill recognize that the list of possible functions that can be performedupon the pair (set) of reconstructed signals include, but are notlimited to, simple math functions such as adding an offset to any or allsignals (positive or negative), multiplying each signal by a constant,functional manipulation of the signals (e.g. Fast Fourier Transform(FFT)), measurement of signal characteristics, multiplication and othermathematical actions of the pair (set) of signals upon one another, etc.Many other actions on the pair (set) of reconstructed signals arepossible and should be considered within the scope of this invention. At348, the resultant signal(s) are displayed.

[0047] Turning now to FIG. 4, which is made up of FIG. 4A and FIG. 4B, awaveform measurement method 400 is shown. It may be helpful to refer toFIG. 3 for an architectural application of this method. This method issimilar to waveform measurement method 200 except that this waveformmeasurement method 400 operates on multiple channels and differs in themathematical processing steps. As such, when reference is made below toany elements of this waveform measurement method 400, the reader canrefer to the discussion above on waveform measurement method 200 of FIG.2 for specifics related to the elements.

[0048] This method starts at 404. At 408, digital signal samples aretaken across all channels. At 412, the digital signal samples areprocessed through a uniform decimator to extract a sample from aspecific position in every time interval for each channel.Simultaneously with 412, at 416, the digital signal samples areprocessed through a dither decimator to extract a sample randomly fromthe time interval for each channel. Likewise, at 420, simultaneouslywith 412 and 416, the digital signal samples are processed through adigital peak detector to extract minimum and maximum samples from thetime interval for each channel. As discussed above, extracting this setof samples allows the potential for compression of the data, therebyreducing storage requirements of the method. As well, this approachpreserves the ability to reconstruct an aliasing resistant signal, whileallowing glitch detection and mathematical functions to be performed onthe reconstructed signal.

[0049] At 424 a decision is made about whether to use all extractedsamples or to select a subset for storage from the extracted samples foreach channel. This determination is based upon the desired intent forthe stored signal samples for each channel. Recalling the discussion inrelation to the configuration select MUX 136 of FIG. 1, thepossibilities for selection apply here as well. If a selection isintended from the extracted samples, this is done at 428 for eachchannel.

[0050] Once the samples that are intended for storage have beenselected, they are stored to a memory at 432 for each channel. Thestored samples are then available for processing and can be retrievedfrom memory at 436 for each channel. At 437, the digital signal samplesare processed through a uniform decimator to allow the extraction of asample from a specific position in every N time intervals retrieved frommemory 116. Simultaneously with 437, at 438, the digital signal samplesare processed through a dither decimator to allow the extraction of asample randomly from every N time intervals. Likewise, at 439,simultaneously with 437 and 438, the digital signal samples areprocessed through a digital peak detector to allow the extraction ofminimum and maximum samples from every N time intervals. As discussedabove, extracting this set of samples allows the potential forcompression of the data, thereby reducing the bandwidth requirements tothe processor 104. As with the previous discussion, all samples can bepassed through each of these portions of the process, or a subset may bepassed through. If raw data were stored to memory 116 at 432 above, thenraw data can be passed through at this point in the process as well.

[0051] At 440, a decision is made about whether to use all retrievedsamples or to select a subset for processing from the retrieved samplesfor each channel. This determination is based upon the desired intentfor the retrieved signal samples. Recalling the discussion in relationto the reduction select MUX 160 of FIG. 1, the possibilities forselection apply here as well. If a selection is intended from theretrieved samples, this is done at 444 for each channel.

[0052] The selected retrieved samples are then used to reconstruct thesignal at 448 for each channel. At 452, a decision is made about whetherto perform a mathematical function on the reconstructed signals. Thisdecision block works in conjunction with the previous two decisionblocks, 424 and 440, such that a uniform decimated sample is stillpresent in the selection set of samples related to the reconstructedsignals if mathematical functions are to be performed on thereconstructed signals.

[0053] If any mathematical functions are to be performed, they are doneat 456. As mentioned above, the mathematical function(s) can be, by wayof example without limitation, simple math functions such as adding anoffset (positive or negative), multiplying the signal by a constant,functional manipulation of the signal (e.g. Fast Fourier Transform(FFT)), measurement of signal characteristics, etc., on eachreconstructed signals. Many other actions on the reconstructed signalsare possible and should be considered within the scope of thisinvention. Furthermore, in this waveform measurement method 400,independent operations on each reconstructed signal are possible as inwaveform measurement method 200, along with additional mathematicalfunctions including inter-operation upon the reconstructed signals ofthe multiple channels. It should be apparent to one skilled in the art,upon consideration of this teaching, that multiple signal addition,multiple signal subtraction, multiple signal multiplication, and manyother mathematical multiple signal operations can be performed on themultiple reconstructed signals in this waveform measurement method 400.At 460, the resultant waveform is displayed and the waveform measurementmethod 400 ends at 464.

[0054] The processes previously described can be carried out on aprogrammed general purpose computer system, such as the exemplarycomputer system 600 depicted in FIG. 5. Computer system 600 has acentral processor unit (CPU) 610 with an associated bus 615 used toconnect the central processor unit 610 to Random Access Memory 620and/or Non-Volatile Memory 630 in a known manner. An output mechanism at640 may be provided in order to display and/or print output for thecomputer user. Similarly, input devices such as keyboard and mouse 650may be provided for the input of information by the computer user.Computer system 600 also may have disc storage 660 for storing largeamounts of information including, but not limited to, program files anddata files. Computer system 600 may be coupled to a local area network(LAN) and/or wide area network (WAN) and/or the Internet using a networkconnection 670 such as an Ethernet adapter coupling computer system 600,possibly through a firewall.

[0055] Those skilled in the art will recognize that the presentinvention has been described in terms of exemplary embodiments basedupon use of a programmed processor. However, the invention should not beso limited, since the present invention could be implemented usinghardware component equivalents such as special purpose hardware and/ordedicated processors which are equivalents to the invention as describedand claimed. Similarly, general purpose computers, microprocessor basedcomputers, micro-controllers, optical computers, analog computers,dedicated processors and/or dedicated hard wired logic may be used toconstruct alternative equivalent embodiments of the present invention.

[0056] Those skilled in the art will appreciate that the program stepsand associated data used to implement the embodiments described abovecan be implemented using disc storage as well as other forms of storagesuch as for example Read Only Memory (ROM) devices, Random Access Memory(RAM) devices; optical storage elements, magnetic storage elements,magneto-optical storage elements, flash memory, core memory and/or otherequivalent storage technologies without departing from the presentinvention. Such alternative storage devices should be consideredequivalents.

[0057] The present invention, as described in embodiments herein, isimplemented using a programmed processor executing programminginstructions that are broadly described above in flow chart form thatcan be stored on any suitable electronic storage medium or transmittedover any suitable electronic communication medium. However, thoseskilled in the art will appreciate that the processes described abovecan be implemented in any number of variations and in many suitableprogramming languages without departing from the present invention. Forexample, the order of certain operations carried out can often bevaried, additional operations can be added or operations can be deletedwithout departing from the invention. Error trapping can be added and/orenhanced and variations can be made in user interface and informationpresentation without departing from the present invention. Suchvariations are contemplated and considered equivalent.

[0058] While the invention has been described in conjunction withspecific embodiments, it is evident that many alternatives,modifications, permutations and variations will become apparent to thoseof ordinary skill in the art in light of the foregoing description.Accordingly, it is intended that the present invention embrace all suchalternatives, modifications, permutations, and variations as fall withinthe scope of the appended claims.

What is claimed is:
 1. A sampling technique for a waveform measuringinstrument, comprising: processing a series of digital signal samplesthrough a uniform decimator to extract at least one uniform decimatedsample value for each sample interval in a first series of sampleintervals; processing the series of digital signal samples through a lowfrequency dither decimator to extract at least one low frequency ditherdecimated sample value for each sample interval in a second series ofsample intervals; and processing the series of digital signal samplesthrough a digital peak detector to extract a maximum sample value and aminimum sample value for each sample interval in the third series ofsample intervals.
 2. A sampling technique for a waveform measuringinstrument as in claim 1, wherein said sample intervals in said first,second, and third series of sample intervals are in phase.
 3. A samplingtechnique for a waveform measuring instrument as in claim 1, whereinsaid sample intervals in said first, second, and third series of sampleintervals are overlapping.
 4. A sampling technique for a waveformmeasuring instrument as in claim 1, wherein said sample intervals insaid first, second, and third series of sample intervals are the samesize.
 5. A sampling technique for a waveform measuring instrument as inclaim 1, wherein said sample intervals in said first, second, and thirdseries of sample intervals are different sizes.
 6. A sampling techniquefor a waveform measuring instrument as in claim 1, wherein said sampleintervals in said first, second, and third series of sample intervalsare out of phase.
 7. A sampling technique for a waveform measuringinstrument as in claim 1, further comprising for each sample intervalstoring at least one of: said uniform decimated sample value; said lowfrequency dither decimated sample value; said maximum sample value andsaid minimum sample value; and said series of digital signal samples. 8.A sampling technique for a waveform measuring instrument as in claim 7,further comprising for each sample interval, retrieving at least one of:said stored uniform decimated sample value; said stored low frequencydither decimated sample value; said stored maximum sample value and saidminimum sample value; and said series of digital signal samples.
 9. Asampling technique for a waveform measuring instrument as in claim 8,further comprising carrying out a reducing process by: processing saidretrieved signal samples through a reducer uniform decimator to extractat least one uniform decimated sample value for each sample interval ina fourth series of sample intervals; processing said retrieved signalsamples through a reducer low frequency dither decimator to extract atleast one low frequency dither decimated sample value for each sampleinterval in a fifth series of sample intervals; and processing saidretrieved signal samples through a reducer digital peak detector toextract a maximum sample value and a minimum sample value for eachsample interval in a sixth series of sample intervals.
 10. A samplingtechnique for a waveform measuring instrument as in claim 9, whereinsaid sample intervals in said first, second, and third series of sampleintervals are in phase.
 11. A sampling technique for a waveformmeasuring instrument as in claim 9, wherein said sample intervals insaid first, second, and third series of sample intervals areoverlapping.
 12. A sampling technique for a waveform measuringinstrument as in claim 9, wherein said sample intervals in said first,second, and third series of sample intervals are the same size.
 13. Asampling technique for a waveform measuring instrument as in claim 9,wherein said sample intervals in said first, second, and third series ofsample intervals are different sizes.
 14. A sampling technique for awaveform measuring instrument as in claim 9, wherein said sampleintervals in said first, second, and third series of sample intervalsare out of phase.
 15. A sampling technique for a waveform measuringinstrument as in claim 9, further comprising for each sample interval:if a mathematical function is selected, performing said selectedmathematical function on said extracted uniform decimated sample valueto create a modified uniform decimated sample value and displaying saidmodified uniform decimated sample value on a display; and if a glitchdetection mode is active, displaying said extracted maximum sample valueand said minimum sample value on a display.
 16. A sampling technique fora waveform measuring instrument as in claim 1, further comprising foreach sample interval: if a mathematical function is selected, storingsaid uniform decimated sample value; and if a glitch detection mode isactive, storing said maximum sample value and said minimum sample value.17. A sampling technique for a waveform measuring instrument as in claim16, further comprising for each sample interval: if a mathematicalfunction is selected, retrieving said stored uniform decimated samplevalue; and if said glitch detection mode is active, retrieving saidstored maximum sample value and said minimum sample value.
 18. Asampling technique for a waveform measuring instrument as in claim 17,further comprising for each sample interval: if a mathematical functionis selected, performing said selected mathematical function on saidretrieved uniform decimated sample value to create a modified uniformdecimated sample value and displaying said modified uniform decimatedsample value on a display; and if said glitch detection mode is active,displaying said retrieved maximum sample value and said minimum samplevalue on a display.
 19. An electronic storage medium storinginstructions which, when carried out on a programmed processor, carryout a sampling technique for a waveform measuring instrument,comprising: processing a series of digital signal samples through auniform decimator to extract at least one uniform decimated sample valuefor each sample interval in a first series of decimated sampleintervals; processing the series of digital signal samples through a lowfrequency dither decimator to extract at least one low frequency ditherdecimated sample value for each decimated sample interval in a secondseries of sample intervals; and processing the series of digital signalsamples through a digital peak detector to extract a maximum samplevalue and a minimum sample value for each decimated sample interval in athird series of sample intervals.
 20. A multi-channel sampling techniquefor a waveform measuring instrument, comprising for each channel:processing a series of digital signal samples through a uniformdecimator to extract at least one uniform decimated sample value foreach decimated sample interval in a first series of sample intervals;processing the series of digital signal samples through a low frequencydither decimator to extract at least one low frequency dither decimatedsample value for each decimated sample interval in a second series ofsample intervals; and processing the series of digital signal samplesthrough a digital peak detector to extract a maximum sample value and aminimum sample value for each decimated sample interval in a thirdseries of sample intervals.
 21. A multi-channel sampling technique for awaveform measuring instrument as in claim 20, further comprising foreach channel and for each sample interval storing at least one of: saiduniform decimated sample value; said low frequency dither decimatedsample value; said maximum sample value and said minimum sample value;and said series of digital samples.
 22. A multi-channel samplingtechnique for a waveform measuring instrument as in claim 21, furthercomprising for each channel and for each sample interval retrieving atleast one of: said stored uniform decimated sample value; said storedlow frequency dither decimated sample value; said stored maximum samplevalue and said minimum sample value; and said series of digital samples.23. A multi-channel sampling technique for a waveform measuringinstrument as in claim 22, further comprising for each channel and foreach sample interval: if a mathematical function is selected, performingsaid selected mathematical function on said retrieved uniform decimatedsample values to create modified uniform decimated sample values anddisplaying said modified uniform decimated sample values on a display;if a multi-channel mathematical function is selected, performing saidselected multi-channel mathematical function on said uniform decimatedsample values for each channel selected for said multi-channelmathematical function to create multichannel modified uniform decimatedsample values and displaying said multi-channel modified uniformdecimated sample values on a display; and if a glitch detection mode isactive, displaying said retrieved maximum sample values and said minimumsample values on a display.
 24. A multi-channel sampling technique for awaveform measuring instrument as in claim 20, further comprising foreach channel and for each sample interval: if a mathematical function isselected, storing said uniform decimated sample values; if amulti-channel mathematical function is selected, storing said uniformdecimated sample values; and if a glitch detection mode is active,storing said maximum sample values and said minimum sample values.
 25. Amulti-channel sampling technique for a waveform measuring instrument asin claim 24, further comprising for each channel and for each sampleinterval: if a mathematical function is selected, retrieving said storeduniform decimated sample values; if a multi-channel mathematicalfunction is selected, retrieving said stored uniform decimated samplevalues; and if said glitch detection mode is active, retrieving saidstored maximum sample value and said minimum sample values.
 26. Amulti-channel sampling technique for a waveform measuring instrument asin claim 25, further comprising for each channel and for each sampleinterval: if a mathematical function is selected, performing saidselected mathematical function on said retrieved uniform decimatedsample values to create modified uniform decimated sample values anddisplaying said modified uniform decimated sample values on a display;if a multi-channel mathematical function is selected, performing saidselected multi-channel mathematical function on said uniform decimatedsample values for each channel selected for said multi-channelmathematical function to create multichannel modified uniform decimatedsample values and displaying said multi-channel modified uniformdecimated sample values on a display; and if said glitch detection modeis active, displaying said retrieved maximum sample values and saidminimum sample values on a display.
 27. A sampling technique for awaveform measuring instrument as in claim 20, further comprisingcarrying out a reducing process by: processing said retrieved signalsamples through a reducer uniform decimator to extract at least oneuniform decimated sample value for each sample interval in a fourthseries of sample intervals; processing said retrieved signal samplesthrough a reducer low frequency dither decimator to extract at least onelow frequency dither decimated sample value for each sample interval ina fifth series of sample intervals; and processing said retrieved signalsamples through a reducer digital peak detector to extract a maximumsample value and a minimum sample value for each sample interval in asixth series of sample intervals.
 28. A sampling circuit in a waveformmeasuring instrument, comprising: a digital peak detector receiving astream of digital signal samples and producing a maximum sample valueoutput and a minimum sample value output for each sample interval of aseries of digital signal samples; a low frequency dither decimatorreceiving said stream of digital signal samples and producing a lowfrequency dither decimated sample value output for each sample intervalof the series of digital signal samples; and a uniform decimatorreceiving said stream of digital signal samples and producing a uniformdecimated sample value output for each sample interval of the series ofdigital signal samples.
 29. A sampling circuit in a waveform measuringinstrument as in claim 28, further comprising: an A/D converterreceiving an analog signal input and producing said stream of digitalsignal samples; a memory that stores at least one of said maximum andminimum sample value outputs, said uniform decimated sample valueoutput, and said low frequency dither decimated sample value output; acompression select multiplexer for selecting at least one of saidoutputs of said digital peak detector, said uniform decimator, and saidlow frequency dither decimator for storage to said memory; a memoryparser for retrieving at least one of said stored digital peak detector,said uniform decimator, and said low frequency dither decimator outputsfrom said memory; a reduction select multiplexer for selecting at leastone of said retrieved outputs of said digital peak detector, saiduniform decimator, and said low frequency dither decimator; and adisplay that displays graphical representation of one of said maximumand minimum sample value outputs, said uniform decimated sample valueoutput, and said low frequency dither decimated sample value output. 30.A waveform measuring instrument, comprising: an A/D converter receivingan analog signal input and producing a digital signal sample output; adigital peak detector receiving an input derived from the A/Dconverter's digital signal sample output, and producing a maximum samplevalue output, and a minimum sample value output; a uniform decimatorreceiving an input derived from the A/D converter's digital signalsample output, and producing a uniform decimated sample value output; alow frequency dither decimator receiving an input derived from the A/Dconverter's digital signal sample output, and producing a low frequencydither decimated sample value output; a memory that stores at least oneof said maximum and minimum sample value outputs, said uniform decimatedsample value output, and said low frequency dither decimated samplevalue output; and a display that displays graphical representation ofone or more of said maximum and minimum sample value outputs, saiduniform decimated sample value output, and said low frequency ditherdecimated sample value output.
 31. A waveform measuring instrument as inclaim 30, further comprising a compression select multiplexer forselecting at least one of the outputs of said digital peak detector,said uniform decimator, and said low frequency dither decimator forstorage to said memory.
 32. A waveform measuring instrument as in claim31, further comprising a memory parser for retrieving at least one ofsaid stored digital peak detector, said uniform decimator, and said lowfrequency dither decimator outputs from said memory, and a reductionselect multiplexer for selecting at least one of said retrieved outputsof said digital peak detector, said uniform decimator, and said lowfrequency dither decimator.